Control system



Nov. 3, 1936. R. M. HARDGROVE Re. 20,156

CONTROL SYSTEM Original Filed May a, 1931 2 Sheets-Sheet 1 INVENTOR. Ralph M. Hardgrove an 9- l fa/r o4 (5 ATTORNEY.

NQV. 3, 1936. HARDGRQVE Re. 20,156

CONTROL SYSTEM Original Filed May a. 19:51 2 Sheets-sheaf 2 Ralph M. Hardqrove m J W fr 2 4 ATTORNEY;

Reissued Nov. 3, 1936 oomor. SYSTEM 7 Ralph M. Hardgrove, Westfleld, N. 1., assignor to The Babcock & Wilcox Company, New York, N. Y., a corporation of New Jersey,

Original No. 2,012,934, dated August 27, 1935,

Serial No. 536.037, May 8, 1931. Application for reissue August 22, 1936, Serial No. 97,472

This invention relates to automatic control systems for pulverizing mills, and more particularly to a control of the quantity and temperature of air which is to provide a carrying means for removing or transporting pulverized material in suspension from the mill.

The quantity of air required to carry the pulverized material in suspension has been found to vary with the type of material, which may be coal, lime, paint pigment or similar substances. and must be sufiicient to transport the pulverized material in suspension without allowing it to drift or settle out in the pipe leading from the pulverizer. It is undesirable, however, to pass through the mill an excess of air over that required. Such an excess requires additional fan or blower capacity at its source as well as additional equipment and expense in separating the pulverized material from the carrier air at the point of usage or storage. If coal to be used as fuel is the material pulverized, then an excess of air may introduce. into the furnace a greater amount or'percentage of air than is desired for efilcient combustion.

7' I havefound it desirable to control the temperature of the carrier air for such a pulverizing mill, so that the material being pulverized will be to a certain extent dried, and as in the case of. fuel pulverized for combustion, any heat added 3o to the air going with the coal to the furnace aids in the economy of operation of the furnace. Said temperatures, however, must be limited to those which are safe from-an operating standpoint of the various apparatus, and with.a consideration of the possibility of spontaneous combustion or volatiiizing of the material. Q

One object of my invention is to provide a sys-' tern of control for the air supplied to a pulverizer, wherein the rate of flow of the air through the 40 pulverizer will be in desired proportion to the rate of feed of material to be pulverized. Another'objectis to so arrange the system-that 'a desirable functio nal relation may exist between the'rate of flow of air and the rate of. feed of material to the pulverizer, and with means formanually adjusting or changing the functional relationship.- a v V A further object is to o limit the minimum flow of air that it cannot'be decreased .below a value wherein is assured the carrying in suspension'oi' the pulverized material.

A still further object is .to so control the temperature of the air passed through the pulverizer that the temperature 'of the mixture of air'and pulverized material leaving the pulverizer will be as desired.

Still another object is to provide an automatic control system for combustion in a steam generating boiler combining a regulation of the input 5 of fuel and air for combustion and to so divide the air supply that a part of it is diverted through a fuel pulverizer to provide a carrier of the pulverized fuel to the combustion chamber.

With these and further objects in view, I will 10 now describe certain embodiments of my invention as illustrated in the drawings.

I have chosen to illustrate and describe my invention with reference to fuel pulverizers for providing an element of combustion for a steam 15 generating. furnace or furnaces, although it will be apparent from a study of the invention and. to those skilled in the art that the invention may be equally applicable to pulverizers of lime, paint pigment or other materials, which for various 20 reasons must be ground or pulverized to a finely divided state and desirably transported by means of air to the point of usage or of. storage.

In the drawings:

Fig. l is a somewhat diagrammatic represents.- 25 tion of a steam generating boiler with fuel and air supplying apparatus to which the invention has been applied. 7

Fig. 2 is a partially sectioned elevation of a pneumatic tachometer.

Fig. 3 is a somewhat diagrammatic drawing of a fuel pulverizer and dischargameans comprising a modification for adaptation to the system illustrated in Fig. l. i

Fig. 4 is a somewhat diagrammatic illustration 36 of a fuel pulverizer system forming a further modification of the complete control system illustrated in Fig. 1. 7

Referring first to Fig. l, I have represented generally at i a steam generating boiler, to the 441 combustion chamber of which is supplied fuel in pulverized form, carried in suspension in a stream of air, and fed to the combustion chamber through a burner 2. A pulverizing mill 3 for reducing the fuel to a finely divided state in which it can be it transported suspended in a stream of air to the boiler, is driven at a constant speed by a motor indicated at 4. Coal to .be pulverized is fed to the pulverizer 3 by ai'eeder 5', driven through a speed adjusting means 6 by an adjustable speed motor 1 Air.to form a carrier for the pulverized fuel and to constitute an element of combustion, is fed to the mill through a conduit 8 under pressure by'a'fan'indicated at$drlven by a constant .l3 relative to the conduits l4 and I5 wherein is available relatively hot and relatively cold airrespectively. I

The temperature of the stream of air carrying the suspended pulverized material to the burner 2 is indicated by a gas-filled thermometer system of which the bulb I6 is located in the path of the stream of air and pulverized material. The bulb is connected by means of a tube ll with a Bourdon tube It having an indicating arm I9 forming the movable element of a contactor for the control or positioning of the reversible motor l3. The motor- I3 is connected by the conductor 20 with the main power line 2|, and through either the conductor 23 or the conductors 24, 25 to the main power line 22.

In the circuit of'the motor I3 'is a two-pole, double throw switch 26, one arm of which is connected to the motor by the conductor 21 and the other by the conductor 29. In the position of rest as shown in Fig. l, the motor is not operating, as the switch 25 is open. The switch is arranged, when moved upwardly, to connect the conductor 21 to a conductor 29 and the conductor 29 to a conductor 30, the conductors 29 and 30 forming branches of the conductor 23 through a selective push button station 3|. When the switch 25 is moved downwardly, the conductor 21 is connected to a conductor 32, and the conductor 29 to a conductor 39, the conductors 32 and 33 comprising branches of the conductor 24 through a selective contactor of which the arm I9 is the selective circuit closer. The conductor 24 is further interrupted before joining the main power line 22, by an interrupting contact arm 34 joiningthe conductor 25.

A positioning of the damper I2 through an operation in one direction or the other of the reversible motor I3 is selectively accomplished by means of the push button station 3| or by the contactor l9, in the one case manually and in the other automatically from variations in temperature at the bulb It. If the switch 26 is in an upper contacting position, then the motor I3 may be energized in one direction or the other by means of the push button station 3| closing circuit between the conductor 22 and either the conductor 29 or the conductor 30. If the switch 26 is in its downward contacting position, then the push button station It is inoperative and energization of the motor l3 may occur only through a closing of circuit between the conductor 24 and the conductor 32 or the conductor 24 and the conductor 33, through a positioning of the contact arm l9 upon a deviation of the temperature of the air and, pulverized fuel mixture temperature from a predetermined value. The contactor I9 is effective, however, only periodically as controlled by a closing of the contact ar'm 34 with the conductor 24 through the periodic rotation of a cam 35 continuously rotated by a motor 36. Thus energization of the motor l3 automatically from temperature deviation, is intermittent or by increments, thereby allowing time for changes in the position of the damper l2 .to become effective upon the temperature at the bulb l6 before further changes in the damper position are made, and thus minimize the tendency toovertravel or hunt.

In addition to the air supplied through the conduit 8 and the burner 2 for transporting the pulverized fuel, further air for combustion is supplied the boiler through a conduit 31 by a fan 39 driven by an adjustable speed motor 39. Products of combustion are withdrawn from the furnace by a fan 40 driven by an adjustable speed motor 4|.

The fuel feeder motor I, the air supply motor 39, and the motor for removing the products of combustion 4|, are connected in parallel to electrical busses 42 and 43, and are arranged to have their speed of rotation varied simultaneously through a control of the voltage supplied the busses. 2| through a conductor 44. The bus is fed from the power line 22 through a conductor 45, inwhich is inserted an adjustable rheostat 45 positioned by a reversible motor 41 connected to the power line2| through the conductors 49, 42, 44 and to the power line, 22 through the conductor 25, said latter circuitcontrolled by a contactor 49 and periodically interrupted by the interrupting contact arm 34, previously described. The contactor 49 is arranged to close circuit for rotation of the motor 41 in one direction or the other upon a departure from a predetermined value of a facpositioning the contactor arm 49 in one direction or the other when the steam pressure within the The bus 42 is fed from the power line boiler l increases or decreases relative to a predetermined desired value.

It will be seen, then, that I have pFvided a means of supplying fuel and air to the boiler l for combustion, depending upon the rate of operation of the boiler, sensitive to variations in a factor of the boiler operation and intermittently effective through the periodic rotation of the cam 35 to minimize the tendency to hunt or overtravel.

I have found that the amount of air supplied for combustion and used in its passage to the combustion chamber as a carrier of the pulverized fuel, should be proportioned to the amount of 'fuel being supplied, although not necessarily directly proportioned thereto. Withthis type of apparatus and under certain conditions of operation, a given amount of air, say 100%, will be needed to transport the maximum fuel pulverized by themill 3, or 100% of fuel, whereas if theboiler is operat-' ing at a rate requiring only 50% fuel, then 50% air would be required as a transport medium. Under other conditions of apparatus and operation, when 50% fuel is supplied it might be advisable to have 75% air, and in any event, when ever fuel is being supplied there should be a minimum rate of feed of the air great enough to prevent drifting or settling out of the fuel from the air stream, or prevent the velocity of the stream from decreasing to a point where flame could travel back from the boiler to the mill. Thus it will beseen that the proportion of air to fuel may be desirably different at different rates of operation, andpreferably there should be provided manually adjustable means for varying the proportionality or functional relation between the supply of air and of fuel.

To properly regulate .the supply of air to the mill 3; it is necessary that an indication be obtained of the rate of flow of the air, and this compared to an indication of the rate of feed of fuel to be pulverized to the mill. I have found that a definite relation exists between the drop in pressure across a portion of the mill 3 and the rate of flow of air and pulverized fuel in suspension through that portion of the mill. In Fig. 1 I have illustrated at 52 the classifying cone of the mill around which the mixture passes from the grinding portion of the mill on its way to the burner 2 and across the restriction of which exists a difierential pressure bearing a quadratic relation to the rate of flow of the mixture.

I have illustrated at- 53 a pipe leading from the outlet of the cone to the inside of a liquid sealed bell 54 and at 55 a pipe leading from the inlet of the cone to the inside of a liquid sealed bell 56. The bells 54 and 56 are hung from a beam 51, pivoted intermediate the points of suspension of the bells at 58, and arranged upon oscillation across the pivot 56 to engage the contact arm 59 with either of the contacts 60 or 6|. The contact arm 59 is adjustably fastened to the beam 51 in a manner such thatthe moment arm relation between the points of connection of the bells 54, 56

d and the fulcrum 56 may be varied.

correspondingly, of the rate of feed of material to be pulverized to the mill.

In Fig. 2 is shown in greater detail the pneumatic tachometer 64 wherein the driven sprocket 65 is connected to and rotates an open-ended cross tube 66 journaled in and pressure-sealed to the pipe 62a. Rotation of the sprocket 65 and of the cross tube 66 throws air by centrifugal force out of the ends of the tube 66, thus creating a suction within the pipe 62:: effective upon the bell 62 to pull it downwardly and thus effect a counterbalance of the beam 51. The law of such a tachometer has been determined as a quadratic relation between speed of rotation and suction produced, so that this efiect may be applied directly as a counterbalance against the similar functional relation of differential pressure between the bells 54 and 56' as an indication of the rate of flow of air through the mill.

By properly selecting the sizes of" the bells 54, 56 and 62, as well as adjusting the fulcrum 58 for moment arm relation of the bells, and the relation of speed between the feeder 5 and the pneumatic tachometer 64, the desired direct or functional relation will exist between the rate of flow of air and pulverized fuel across the cone 52 and the rate of feed of material to be puiverized through the feeder 5. Deviation from such desired relation will cause the contact arm 59 to engage either the contact point 60 or 6| to result in an energization of the motor I I in one direction or the other to correct the rate of flow of air throughthe mill.

The contact 60 is connected through the conductor 1|, the limit switch64a, and the conductor 65a with one pole of a double pole, double throw switch 66a for selecting between push button or automatic operation of the motor I. The limit switch 64a is positioned by a cam 61 moved in step with the damper- ID to break circuit between the conductors 1|, 650. when a predetermined minimum damper position is reached and to prevent a further closing of .the'damper.

The motor II is joined to the power line 2| directly by a conductor 66 and indirectly by the conductors 69 and 10 which lead to the two arms of the selective switch 66a. The contact 6| is joined to one pole of the switch 660 by a conductor as. The main power line 22. is led to the 'switch 66a by a conductor 14 branching through the conductors 12. and 13 and the selective push button station 15.

If the selective switch 66a is positioned toward the right in Fig. 1, circuit will be closed through the conductors 69 and 63 to thecontact 6|, and through the conductors 19, 65a, limit switch 641: and conductor 1| to the contact 66. Thus the motor ll, one side of which is directly connected with the power line 2| through the conductor 68, is connected for selective contact by the arm 59, whichthrough a conductor 16, interrupting contact arm 11 and conductor 25 is joined to the main power line 22, periodically upon rotation of the cam 18 which is driven in parallel with the cam 35 by the motor 36.- i

When the switch 660 is thrown to its contacting position to the left in Fig. 1; then the motor is connected through the pushbutton station 15 and disconnected from the contact points 66 and 6|, to the end that the push button 15may be operated to connect the power line 22 through the conductor 12 to the conductor 69, or through the conductor 13 to the conductor 16, and rotate the motor in one direction or the other as,

desired, manually trol.

In operation, assume for example, that the steam output of the boiler increases and the steam pressure decreases. The decrease in steam pressure will result in a tendency toward a counter-clockwise rotation of the contact arm 49 of the Bourdon tube 5|, to cause engagement with one of the terminal contacts of the motor 41 for a rotation thereof." The motor 41, however, will be energized only intermittently upon closure of circuit through the contact arm 34 by rotation of the cam 35. Thus, so long as the contact arm 43 engages one of the terminal contacts of the motor 41, the motor 41 will be operated by increments to vary the adjustment of the rheostat 46 and thereby the speed of the fuel motor 1, the air supply motor 39 and the motor 4| which removes the products of combustion from the boiler. The supply of the elements of-combustion to the boiler will be increased, and by increments of duration as determined by the percentage of each revolution of the cam 35 that by remote push button conthe contact arm 34 is close circuited, and by the of overtraveling and hunting. Should the load decrease and the pressure rise above the predetermined desirable value, the action of the contactor is the reverse, and the motors 1, 39, and 4| would be decreased in speed, with a corresponding decrease in rate of feed of fuel and air for combustion.

Considering the first condition, namely, an increase in speed of the fuel feeding motor 1 and of the feeder 5, this will result in an increase in speed of rotation of the pneumatic tachometer 64, a corresponding increase in suction within the bell 62, causing the same to move downward and oscillating the beam 51 to move the contact arm by increments asdetermined by the rotation of the cam II. An increase in the rate of flow of air through the conduit 8 to the mill will result in an increased velocity past the coneil, an increased diil'erential pressure between the pipes I and 53 and correspondingly below the bells 56 and I4, which means that the upward push of the bell It will have greater preponderance over the upward push of the bell 54 than previously, and this eifect will increase until it counterbalances the eflect of the downward pull of the bell 62 and causes the contact arm 59 to. seek its neutral non-contacting position wherein the relation between the pressure differential across the cone 52 and suction produced by the pneumatic tachometer I4 is in equilibrium.

In the arrangement illustrated in Fig. 1, the pressure transmitted through the pipes 53 and ll will be higher than atmosphere, but it is understood that it is immaterial whether the pressures eil'ective upon the bells 54 and 56 are greater or less than atmosphere, as it is relative pressures or pressure differential that produce the result.

Regardless of rate of operation of the boiler I, or changes. in such rate and corresponding changes in the rate of supply of material and carrier air to the mill 3, the heat content of the air supplied through the conduit 8 is adjusted to maintain a desired temperature of the mixture of air and pulverized fuel in suspension leading to the burner 2. Assume the selective switch 26 to be in the automatic position (downward), and that for some reason the temperature of the mixture passing the bulb it has lowered below that which is desirable, then the Bourdon tube ll will tend to close up in a clockwise direction,

and result in a rotation of the motor I! in a direction to cause an admission of a greater proportion of cooler air to warm air, the rotation of the motor it being intermittent through pe riodic rotation of the cam 35.

It will be seen that both in the case of the positioning of the damper l and the positioning of the damper I! for control respectively of the quantity and of the temperature of the air supplied as a carrier of the pulverized material, I have the possibility through the selective switches II and a of having either automatic control or remote manual push button control of the said dampers.

In Fig. 3 I have illustrated a modification of a fragment oi the layout shown in Fig. 1, like parts bearing the same reference numerals. In this modification, air is supplied the-mill through the conduit 8 from any desirable source, whichmay be the atmosphere or may be from a heater or. heat-controlled device, but the conrol of the quantity of air supplied the mill 3 is not in the conduit 8 as is the case in Fig. l. positioned between the mill. 3 and the burner I a fan 19 driven by an adjustable speed motor 8|, exhausting from the mill 3 air and pulverized fuel carried in suspension by the air. The pressures effective through the pipes 53 and 55 are in this embodiment less than atmospheric. The control of the air flowing through the mill 3 is by speed control of the motor 80 rather than by positioning of a damper in the conduit 8.

To control the speed of the motor 80.1 have provided a rheostat 8| positioned by a reversible motor 82 in a manner similar to the positioning of the damper It by the reversible motor ll of Fi 1.

It will be seen that my invention is equalb applicable to pulverized material supplying systems and pulverizing mills operated under a suction as to those operated under a pressure of the air, and whether the air is forced through the 'mill or drawn through the mill by an exhauster.

In Fig. 4 I have shown somewhat diagrammatically a further modification illustrated as a fragment of the layout of Fig. 1 depicting a different type of mill, namely one commonly known as a horizontal ball mill, as compared to the vertical ball mills of Fig. 1 and Fig. 3, and further, with somewhat different arrangements of control, but to accomplish a similar purpose in volume and temperature control of the air passing through the mill as acarrier for the pulverized material.

The mill 3a is rotated through the gear a by any suitable means (not shown) and'is trunnion-mounted at the bearings 84 in a manner such that the fuel admission pipe I! enters at one end, and the air admission conduit 8A enters at the other end, without objectionable leakage of air or pulverized material and without interfering with the free rotation of the mill in.

The rate of admission to the mill of coal to be pulverized is controlled by the positioning across the admission duct 86 of a gate 88 through movement of a rack 81 by a gear 88 fastened to a shaft 89. An exhauster motor 19A pulls the mixture of air-and pulverized material in suspension irom the mill through a conduit 90 so formed to join the conduit 8A and an inner conduit 9| which lies within the conduit IA and extends to the'interior of the mill la. Air passing through the conduit 8A may pass through the I have shown mill 3a around the conduit extension 9|, or may bypass the mill directly to the conduit III, depending upon the positioning (vertically in the the mill 3a around the inner conduit 8| returns through the conduit 9| with the fuel carried in suspension and passes to the exhauster IDA through the conduit 80 along with any air which has been bypassed directly from the conduit IA to the conduit 90, depending upon the positioning of the gate 92. Thus it will be seen that if the gate 92 is in its uppermost position, none of the air from the conduit 8A is bypassed directly to the conduit 90, but all of said air passes to the mill and to the conduit 90 through the inner conduit 9|; whereas if the gate 82 is positioned to its lowermost position on the drawing, then all I drawing) of a gate 92. All of the air entering oi the air passing through the conduit 8A is by The gate 02 is controlled in vertical position by the rotation of a screw-threaded rod 09 in turn rotated from the shaft 00. The shaft 09 is turned when desired through an energization of the motor "A which corresponds to the motor 01 of Fig. 1. The position of the gate 06, indicative of the rate of feed of fuel to the mill, and of the gate 02, both controlled by the position of the shaft 00, is in this embodiment dedrably remotely indicated for comparing with the rate of flow of air the mill, by means of selfsynchronous or w motors, generally indicated at and 00. I vd ate at 90 a transmitting Ienerator and at 05 a receiving motor. The transmitting generator is operated at a suitable ratio with respect to the gate 06 by means of .lpur gears connecting the generator shaft 96 to the shaft 00. Rotor shaft 91 of the receiving motor positions angularity an arm 90 from which is freely suspended a link 99.

The generator and motor are similar in construction, having single phase field windings, I and IOI on the rotors, and three-phase armature windings I02 and I09 on the stators. Thevfleld windings .are energized from a suitable source of alternating current supply 2| and 22, while like points of the armature windings are interconnected.

The operation of systems of this general character for the transmission of angular movement is well known in the art. Voltages are induced in the three-phase stator windings of the generator and motor by the single phase field windings on the associated rotors. When the rotors of the generator and motor are in the same angular position with respect to their stators, the induced voltages in the armature windings are equal and opposite, and consequently no current is set up in the armature windings. If the rotor of the generator is turned and held in its new position, the voltages no longer counterbalance, whereby equalizing currents are caused to flow in the armature windings. The equalizing currents exert a torque on the rotor of the motor, causing it to take up a position corresponding to the position of the generator rotor. Angular movement imparted to generator 94 is therefore reproduced by receiving motor 95. When the shaft 89 is rotated, a proportional rotation occurs in angular movement of the arm 98, remotely located in the present embodiment at a point adjacent a measuring means .of the rate of flow of air to the mill.

In the present embodiment I measure the air to the mill in by means 10f a flownozzle I00 or other similar pressure difierential .producing device, at opposite sides of which to the conduit 0A are Joined the pressure pipes 53A and "A, leading respectively to the underside of the liquid sealed bells 54A and 56A suspended from the pivoted beam 51A in a manner similar to that illustrated in Fig. 1. I desire, however, to translate the quadratic relation of, pressure difierential relative to flow, through the flow nozzle I04 to increments of flow for the positioning of the beam 51A, so I suspend from the beam 51A in addition to the bells 54A and 56A, a variable counterba'lancing means comprising a displacer I00 submerged in varying amount in a liquid such as mercury and effecting -a variable counterbalancing of the differential pressure applied to the beam A. From the beam 51A a link I00 is freelg suspended, and is positioned vertically directly in proportion to the rate of flow of air supplied to the mill 3a.

Freely from the lowermost ends oi the vertical links 99 and I06 is a floating bar I01,

from a point intermediate the ends of which is tact II2 results in an operation of the motor IIA in one. direction or the other for a positioning of the damper MA to control the total supply of air to the mill.

It will be apparent to those skilled in the art, that should the rate of feed of fuel and air to the pulverizer increase or decrease in step with each other, then the vertically suspended links 99 and I06 may be arranged to move oppositely and equally to the end that the center point of. the floating bar I01 will be unchanged imposition, and the vertical link I08 will not be moved vertically, and no rotation of the motor I IA will result, for the relationship between air and fuel is as desired.

If, however, the rate of fuel feed is increased through movement of the motor A, then the position of the shaft 89 being remotely transmitted to cause an angular positioning of the arm 98 will move vertically the link 99 irrespective of the fact that the link I06 has not been so moved, and the result will be a vertical positioning of the link I08 and a closing of either the contact I I I or the contact II2 to result in an operation of the motor IIA, varying the rate of flow of air through the conduit 0A. This change in the rate of flow of air efiective across the flow nozzle I 04 will change the pressure differential effective upon the bells 54A and 56A, with the result that the vertical link I06 will be positioned vertically and in opposite direction to that of the link 99. Thus when the air flow has been changed in amount in desired proportion to the rate of fuel feed, the Contact am I09 will be brought back to its original non-contacting position and further change in the position of the damper I 0A will cease.

It will be seen that the modifications illustrated in Fig. 3 and Fig. 4 form modifications of a part only of the complete system illustrated in Fig, l, and may be substituted in the complete system illustrated in Fig. l for the parts of which they are modifications. To save unnecessary duplication, howe Ier, Fig. 3 and Fig. 4 have been drawn to illustrate only the parts so modified rather used as a fuel in a boiler furnace, but for other materials wherever it is desirable to transport the pulverized material from the mill by means of carrier air and control the proportion of the,

carrier air to the rate ,of feed of material to the mill, or control the temperature of the carrier air to maintaina desired temperature of the mixture of carrier air and material transported in suspension in pulverized form.

Having now described certain preferred embodiments of my invention, I desire it to be understood that I am not limited thereby, other'than as claimed in view of prior art.

What I claim as new and desire to secure by Letters Patent of the United States, is:-- t

1. In a pulverizing apparatus, a pulverizing mill including means for feeding thereinto material to be pulverized, means for supplying air to the mill to carry therefrom the pulverized material in suspension, means for bypassing directly tothe discharge of the mill part or all-of the air supplied, means for simultaneously varyingthe proportion of air so bypassed and the rate of feed of material to be pulverized, measuring means of the air supplied, means for varying the quantity of air supplied, regulating means for said last-named means, and control means responsive to said third-named means and said measuring means for positioning said regulating means when other than a predetermined relation exists between the rate of supply of air and material to be pulverized.

2. In a pulverizing apparatus, a pulverizing mill including means for feeding thereinto material to be pulverized, means for supplying air to the mill to carry therefrom the pulverized material in suspension, valve means associated with said air s pp ying means for varying the quantity of air supplied, control means for effecting movement of said valve means comprising a reversible electric motor, a contact means for energizing said motor, measuring means of the air supplied, a transmitting generator positioned responsive to the rate of feed of material to be pulverized, a receiving motor for indicating the rate of feed of material to be pulverized, alternating current field and armature windings for said motor and generator,

electrical connections for equalizing currents between said armature'windings whereby the motor is caused to be in synchronism with the generator, said receiving-motor and said measuring means coacting to position said contact means for operation of the reversible electric motor in one direction or the other when the rate of flow of air supplied and rate of feed of material to be pulverized deviates from desired proportionality.

3; In a pulverizing apparatus, a pulverizing mill including means for feedingthereinto material to be pulverized, means for supplying air to the mill to carry therefrom the pulverized material in suspension, valve means associated with said air Supplying means for varying the quantity of air supplied, control means for effecting movement of said valve means comprising a reversible electric moto a contact means for energizing said motor, measuring means of the air supplied, a transmitting generator positioned responsive to the rate of feed of material to be pulverized, a

receiving motor for indicating the rate of feed of material to be pulverized, alternating current field windings for said motor and generator, asource of alternating current supply for said field windings, poiyphase armature windings for said motor and generator, electrical connections between said armature windings whereby the motor is caused to be in synchronism with the generator, said receiving motor and said measuring means coacting to position said contact means for operation of the reversible electric motor in one direction or the other when the rate of flow of air ferent at different rates of operation of the pulfollowing the removal of said limitation.

-mill, control means for varying the speed of the fan, and automatic means responsive to the rate 10 of feed of material to the mill for positioning said control means.

5. In a pulverizing apparatus, a pulverizing mill including means for feeding thereinto material to be pulverized, means for supplying air to the mill suspension, control means for said air supplying means, means continually determining the rate at which the material is supplied to the pulverizer, automatic means responsive to said last-named means for positioning said control means, means limiting the said automatic means whereby the rate of supply of air cannot be reduced below a predetermined minimum, manually operated means for making inoperative said limiting means whereby the limitation of reduction in the rate of flow of air is removed, and manually operated meanswhereby the rate of flow of air may be decreased below said predetermined minimum 6. In a fuel preparing and handling system, the combination of a' pulverizing mill including means for feeding thereinto fuel to be pulver ized, means for supplying air to the mill to provide a carrier for the pulverized fuel, a discharge conduit for the pulverizer and through which the stream of carrier air and pulverized fuel in suspension is passed, control means for said air supplying means, automatic means jointly responsive to the rate of feed of fuel to the mill and to the rate of flow of air through the mill for positioning said control means, and thermostatically controlled means for maintaining 'a predetermined temperature of the stream of carrier air and pulverized fuel in suspension passing through the conduit. j

7. In a fuel preparing and handling system, the combination of a pulverizing mill including means for feeding thereinto fuel to be pulverized, means for supplying air to the mill to provide a carrier for the pulverized fuel, a discharge conduit for the pulverizer and through which the air and pulverized fuel in suspension is passed,- means for bypassins a portion of the air directly to the conduit, and control means for simultaneously varying the rate of supply of fuel to pulverizer and proportionally varying said passing of air.

8. In a fuel preparing and handling system, the combination of a pulverizing mill including means for feeding thereinto fuel to be pulverized. means for supplying air to the mill to provide a carrier for thepulverized fuel, a discharge con duit for the pulverizer and through which the air and pulverized fuel in suspension is passed. means for bypassing a portion of the air directly to the conduit, control means for simultaneously varying the rate of supply of fuel to the pulverizer arid proportionally varying said bypassing of air, and automatic means responsive to the rate of supply of fuel to the pulverizer for controlling the total supply of air.

9. In ,afuel preparing and handling system,

to carry therefrom the pulverized material in r the combination of a pulverizing mill including means for feeding thereinto fuel to be pulverized, means for supplying air to the mill to provide a carrier for the pulverized fuel, a discharge conduit for the pulverizer and through which the air and pulverized fuel in suspension is passed, means for bypassing a portion of the air directly to the conduit, control means for simultaneouslyvarying the rate of supply of fuel to the pulverizer and proportionally varying said bypassing of air, and thermostatic means responslve to the temperature in the conduit for controlling the temperature of the air supply.

10. In a pulverizing apparatus, a pulverizing mill including means for feeding thereto material to be pulverized, means for supplying air to the mill to provide a carrier for the pulverized material, control means for said last-named means, an air flow meter, and a meter of the rate of-supply of material to the pulverizer, said meters conjointly effective in positioning said control means. 10

RALPH M. HARDGROVE. 

